346 



Allen and Crenshaw — Sulphides of Zinc, 



Table II. 

 Inversion- of pure natural zinc sulphide. 





Time. 



1 



4 hrs. 



2 



8} " 



3 



4 " 



4 



4i " 



5 



3f " 



6 



9| " 



Temp, in my. 



9950 El. A. 

 9650 El. A. 

 9850 El. A. 

 980Q El. A. 



9750 El. A. 

 9700 El. A. 



Result. 



j Wurtzite unchanged. 



J Sphalerite about -J changed. 



" unchanged. 



" slightly changed. 



" very slightly changed. 



i Wurtzite slightly, if at all, 

 changed. 

 Sphalerite unchanged. 



j Sphalerite unchanged. 

 ] Wurtzite partly changed. 



In four hours at 800° there was no appreciable change in 

 wurtzite. It required 66 hours, between 800° and 900°, to 

 change the mineral entirely into sphalerite. In a repetition of 

 the experiments, 48 hours were required for the change at 

 850° -900°, and again 40 hours at 850° -950°. For these ex- 

 periments we used both the wurtzite formed by heating pure nat- 

 ural sphalerite and also some natural wurtzite crystals from the 

 Hornsilver Mine near Frisco, Beaver Co., Utah, which behaved 

 in the same way. 



Effect of iron on the inversion point of zinc sulphide. 



It is well known that the natural sulphide of zinc nearly 

 always contains sulphide of iron (FeS), sometimes in quantities 

 as high as 20 per cent or more. The effect of this common 

 impurity on the inversion point" was thought to be of interest, 

 and accordingly several iron-bearing sphalerites which con- 

 tained only small quantities of other impurities were carefully 

 analj'zed and tested thermally. 



Ferrous sulphide lowers the inversion point of sphalerite 

 strongly as the results in Table III show. From fig. 2 it will 

 be seen that the inversion temperatures when plotted against 

 the percentages of iron form a fairly regular curve. It ought 

 to be noted, however, that blende containing other impurities 

 besides iron sulphide does not always show a lower inversion 

 temperature than pure sphalerite. Thus a blende from 



